Method of coating metal articles with zinc



Patented Nov. 23, 1937 METHOD or coarnvc METAL narrows WITH ZINC

Allan Heathcote Williams, Chester, England No Drawing. Application March16, 1937, Se-

rial No. 131,183. In Great Britain August 9, 1935 1 Claim.

This invention relates to an improved method of and means forcoatingmetal articles with zinc, and has for its chief Object to provide animproved process by means of which metal win- 5 dow frames may be veryeffectively and efliciently galvanized although, as will be appreciatedfrom the following description, the present invention is by no meanslimited to a process for galvanizing metal window frames but is alsoapplicabl to the galvanizing of other metal articles. The process ofgalvanizing a metal article according to the present invention ischaracterized in that the article to be galvanized is first given acoating of zinc by immersion in a bath of molten zinc, which coating isthen heated out of ,contact with oxygen, or other gas or substancelikely to have an injurious effect on the coating,

for such a time and to such a temperature that the coating forms analloy with the metal to .be coated and is finallywhilst still hotimmersed inmolten zinc, without contact with oxygen or other injuriousgas or substance, whereby a coating of zinc firmly adhering to thepreviously produced alloy is obtained.-

The apparatus for carrying out the present invention convenientlyconsists of a bath, the major portion of which is filled with moltenlead or some other suitable substance of higher specific gravity thanspelter, a comparatively thin layer 30 of molten spelter floating on topof the lead or the like. The articles to be coated are passed throughthe spelter into the molten lead where they are allowed to remain untilthey acquire the requisite temperature to enable the zinc to form analloy with the surface of the metal. The articles are then withdrawnthrough the layen oi. spelter where they receive a further coating ofzinc.

The bath is preferably narrower at the bottom than at the top and hasthe heat applied to the sides of the same so that the heat lost onimmersion of an article may be quickly 7 made up.

- When molten spelter is heated to a sufliciently high temperature toenable it to forman alloy with the article to be coated, it tends toattack the iron walls of the spelter bath and so rapidly increases theformation of dross and consequent wastage of spelter. To a very largeextent this disadvantage is overcome in the apparatus according to thepresent invention due to the relatively thin layer of zinc employed but,if desired, the spelter may be contained in a relatively shallowretaining frame having its walls partly imsame temperature orapproximately the same (Cl. ill-20.2)

mersed in the lead and having a clearance from the sides of the tank. a.

, at the top at its widest part. The bath is about seven feet deep andtapers downwardly so that 0 it is only about one foot wide at thebottom. By this means the heat ofthe furnace which is arranged on thesides of the bath is distributed over a wide area of the bath (which isconveniently made of iron) and so the heat lost on the immersion of thearticle to be galvanized'into the bath can be quickly made up.

The bath is filled to the extent of about ninetenths of its depth, viz.,about six feet four inches, with molten lead or other suitable metal andon top of this molten lead or the like floats a layer of about eight orten inches of molten zinc.

In use the window frame, or other article to be galvanized is, afterbeing suitably pickled in the usual way, passed quickly through the thinupper layer of molten zinc into the molten lead beneath the same.Thearticle is then allowed to remain in the molten lead until itacquires the temperature as the molten lead which is conveniently heatedto about 550 5'70 C. During this time and when the article attains atemperature of about 490? C. the pores of the metal article seem to openand the preliminary coating of zinc which the article has received dueto its initial passage through the molten zinc appears to form an alloywith the iron of the article to be galvanized. V

Whenthe article has attained the desired'temperature it is withdrawnfrom the bath, passing again through the thin layer of zinc at the topof the bath. A skin-bond is formed through the zinc entering into thepores of the iron of the article to be galvanized and the coating ismuchmore firmly attached than with the ordinary process of hot zincgalvanizing as carried out at the present time. For example, with theordiwhich will prevent it coming into contact with the sides of thebath.. I r ,4

The invention is capable of general application for zinc coatingarticles, but is particularly intended for forming a zinc coating onmetal window frames which are very liable to rust.

I claim:--- 7 A method of coating metal articles and more particularlywindow frames with zinc carried out 10 in a bath comprising athin layerof molten zinc l 1 I I

